There are, of course, numerous applications where movable arms are employed for supporting one or more articles. By way of example, a multitude of structures has been disclosed for use in home, office, medical, and other applications wherein a lamp is supported by one or more articulated arms. Other articulated arm arrangements have been disclosed for supporting magnifying arrangements of various sizes, weights, and configurations. Still other arm arrangements have been particularly designed for providing adjustable support to computer monitors and similar articles.
In these and further articulated arm structures, a most fundamental goal is to support the retained article in a state of perfect equilibrium over a broad range of adjustment of the angular disposition of the arm or arms. What may be considered the ultimate goal is to enable the angle at which the arm or arms are disposed to be adjusted by the application of a minimal motive force even where the retained article is of a relatively significant weight. With this, designers of the prior art have sought for many years to develop an arm arrangement that can retain an article in an equipoise relationship over an infinitely variable range of angles that can be moved from equipoise position to equipoise position with the application of the slightest motive force.
For a plurality of reasons, however, the creation of such an ideally performing mechanical arm arrangement has proven elusive. One fundamental challenge that has confronted inventors of the prior art derives from the fact that, as the angle of a support arm changes relative to vertical, the resistive force required to retain it in an equipoise condition will necessarily vary as well. Accommodating that changing moment arm is rendered particularly difficult in a mechanical arm arrangement since it varies over a nonlinear sine curve as the angular disposition of the support arm is progressively increased or decreased.
Numerous prior art devices have sought to provide the required counterbalancing force by means of one or more resiliently compressible or extendible members, such as coil springs or elastic members, appropriately interposed in a parallelogram arm arrangement. The use of such spring arrangements can be effective to an extent since the springs can be arranged to demonstrate resistance that increases or decreases in general correspondence to the force required to support the retained article. However, over its elastic range, the force required to stretch or compress a spring varies linearly pursuant to the spring constant. As a result, the linear resistance imparted by an unobstructed spring of a given length fails to correspond to the nonlinear downward force of the retained article as the support arm is moved through a given angular range. Consequently, even when a spring arrangement has been specifically designed to support a given weight, the spring or springs will tend to provide excessive resistance over one or more portions of the arm's range of motion while providing too little resistance over one or more other portions of the arm's range of motion. With this, although highly desirable, crafting an arm arrangement capable of supporting an article in a state of equipoise over a broad range of arm angles has been notably difficult.
A plurality of additional issues and considerations further complicate the design and manufacture of equipoise support arms. One significant consideration derives from the fact that equipoise arms must support articles of differing weights. In certain designs, a given arm skeleton will be employed for supporting differently weighted articles by substituting springs with spring constants calibrated to suit the particular weight to be supported. However, it will be appreciated that such a practice leads to a plurality of complications. For example, the manufacturer must keep a stock of all possible springs, and confusion between marginally different springs must somehow be avoided. A further design issue derives from the fact that electrical power often must be provided to the supported article such that wiring must normally traverse the support arm or arms thereby harming the aesthetics of the arm construction and possibly interfering with the function of the arm or arms. Even further, in many prior art arrangements, each arm is founded on a parallelogram formed by multiple exposed bars that can pinch and otherwise pose a potential danger to the user.
In light of the foregoing, it becomes clear that there is a cognizable need in the art for a truly obedient arm assembly that can be moved with the application of the slightest motive force while accommodating the nonlinear change in moment arm presented by the arm or arms over a broad range of angles. It will be additionally appreciated that there are further distinct needs for an obedient arm assembly that is capable of accommodating articles of differing weights, that can shield wiring from view and damage, and that can avoid presenting any danger to the operator. It will be clearer still that an obedient arm assembly providing a solution to each of the needs and problems described above while providing a plurality of advantages thereover would represent a marked advance in the art.